向量C ++中字节表示形式的int

Question

I have a vector<int> of length n which contains only 0 and 1's. For example we can have the following vector of length 10:

0 1 1 0 1 0 0 1 0 0

Now I use the number represented by that vector to access a location in an array with 2^n entries (so in this case an array of 2^10 = 1024). I'm not sure how I can obtain one integer from the byte representation stored in this vector<int> .

Answer 1

Simply run through the vector and collect powers of 2.

It depends on which end of the vector you want as most significant digit but eg

auto to_int( const vector<int>& digits )
    -> int
{
    int result = 0;
    for( int const digit : digits )
    {
        result += 2*result + digit;
    }
    return result;
}

Or the other way,

auto to_int( const vector<int>& digits )
    -> int
{
    int result = 0;
    for( int i = (int)digits.size();  i --> 0; )
    {
        result += 2*result + digits[i];
    }
    return result;
}

Disclaimer: code not reviewed by compiler.

Answer 2

使用具有to_ulong（）方法的std :: bitset（ http://en.cppreference.com/w/cpp/utility/bitset ）

Answer 3

A simply way using a for loop:

size_t val{0};
for (const auto i : vec)
    val = (val << 1) + i;

Answer 4

Something like this:

int integer=0;
int c=0;
for(int i : intVector){
    integer+=i<<c;
    c++;
}
return integer;

Answer 5

You can keep the std::vector and use std::bitset :

#include <iostream>
#include <vector>
#include <bitset>
#include <algorithm>
#include <climits>

template <typename IterType>
unsigned long getValue(IterType i1, IterType i2)
{
    unsigned long i = 0;
    std::bitset<CHAR_BIT * sizeof(unsigned long)> b;
    std::for_each(i1, i2, [&](auto n) { b.set(i++, n);});
    return b.to_ulong();
}

int main() 
{
    std::vector<int> v = {0, 1, 1, 0, 1, 0, 0, 1, 0, 0};
    auto val = getValue(v.rbegin(), v.rend());
    std::cout << val << "\n";;  
    auto val2 = getValue(v.begin(), v.end());
    std::cout << val2;  
}

Note that depending on which bit is the most significant bit, you supply the iterators accordingly. For right-to-left, supply reverse iterators, otherwise supply forward iterators.

Live Example